A non-fluorine-coated separator and a method for manufacturing the same, a secondary battery

Abstract

The application provides a non-fluorine-coated diaphragm, a preparation method thereof, and a secondary battery. The non-fluorine-coated diaphragm comprises a base film and a composite coating layer coated on at least one side of the base film. The composite coating layer comprises a first coating layer and a second coating layer, and the first coating layer is arranged between the second coating layer and the base film. The first coating layer comprises first inorganic particles and second inorganic particles. The second coating layer comprises third inorganic particles and polymer particles. The polymer particles are non-fluorine polymers. The lower surface of the polymer particles is tangent to the first coating layer, and the polymer particles are filled in the second coating layer. When the temperature in the battery cell rises, the non-fluorine-coated diaphragm can effectively block the charging and discharging of the battery cell. When the temperature in the battery cell returns to normal, the swelling of the polymer particles decreases, the coverage of the polymer particles in the composite coating layer decreases, and the battery cell can operate normally again. The non-fluorine-coated diaphragm does not deteriorate the internal resistance and cycle performance of the battery cell, and simultaneously improves the heat resistance of the non-fluorine-coated diaphragm at high temperatures.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a non-fluorine coated separator, its preparation method, and a secondary battery. Background Technology

[0002] As an important part of the battery, the separator can isolate the positive and negative electrodes and prevent short circuits between them, while allowing ions to pass through. Therefore, the performance of the separator affects the performance of the battery cell. For example, the heat resistance of the separator directly affects the safety of the battery cell at high temperatures. A separator with high heat resistance reduces the risk of short circuits at high temperatures.

[0003] As battery capacity increases, cell safety has become a growing concern, leading to the development of flame-retardant separators. Current technologies often incorporate flame-retardant materials into the coated separator, such as low-melting-point polymers. When the temperature rises to the melting point, the polymer melts and plugs the pores, preventing thermal runaway. Alternatively, polymers that release inert gases are added; when the temperature reaches a certain level, the polymer decomposes and releases the inert gas, also preventing thermal runaway. However, these methods are irreversible; once triggered, the cell must be discarded. In practical applications, during prolonged charging and discharging, the internal temperature of the cell sometimes rises rapidly. When using a flame-retardant separator, the flame retardant melts or releases gas, hindering the cell's charging and discharging. When the internal temperature returns to normal, this triggered flame-retardant polymer significantly impacts the cell, severely degrading its performance, increasing internal resistance, and drastically worsening cycle performance.

[0004] Furthermore, existing flame-retardant separators can only rapidly block the battery cell from running out of control, which deteriorates the heat resistance of the coated separator itself at high temperatures. Therefore, there is an urgent need for a coated separator that can effectively block the charging and discharging of the battery cell when the internal temperature rises, and does not deteriorate the internal resistance and cycle performance of the battery cell when the internal temperature returns to normal, while improving the heat resistance of the coated separator at high temperatures.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a non-fluorine coated separator and its preparation method, as well as a secondary battery. When the internal temperature of the battery cell rises, the non-fluorine coated separator can effectively block the charging and discharging of the battery cell. When the internal temperature of the battery cell returns to normal, the swelling of the polymer particles decreases, the coverage of the polymer particles in the composite coating decreases, and the battery cell can resume normal operation. The non-fluorine coated separator does not deteriorate the internal resistance and cycle performance of the battery cell, while improving the heat resistance of the non-fluorine coated separator at high temperatures.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] A non-fluorine coated membrane includes a base membrane and a composite coating coated on at least one side of the base membrane, the composite coating including a first coating and a second coating, the first coating being disposed between the second coating and the base membrane;

[0009] The first coating comprises first inorganic particles and second inorganic particles;

[0010] The second coating comprises third inorganic particles and polymer particles;

[0011] The polymer particles are non-fluoropolymers;

[0012] The lower surface of the polymer particles is tangent to the first coating and fills the interior of the second coating.

[0013] Furthermore, the maximum number of polymer particles connected in phase is N, where N≤8.

[0014] Furthermore, the coverage of the polymer particles in the composite coating is η1, where 20% ≤ η1 ≤ 35%.

[0015] Furthermore, the non-fluorine coated diaphragm is immersed in an electrolyte at 60°C for 4 hours and then cooled, and the coverage of polymer particles in the composite coating is η2, where 23%≤η2≤37%.

[0016] Furthermore, the non-fluorine coated diaphragm is immersed in an electrolyte at 120°C for 4 hours and then cooled, and the coverage of polymer particles in the composite coating is η3, 38%≤η3≤53%.

[0017] Furthermore, the thickness of the first coating is H1, the thickness of the second coating is H2, 0.5≤H1≤1.0μm, and 0.8≤H2≤2.0μm.

[0018] Furthermore, the wet pressure adhesion force between the non-fluorine coated diaphragm and the electrode sheet is ≤0.5N / m.

[0019] Furthermore, the polymer particles have a core-shell structure, comprising a core layer and a shell layer.

[0020] Furthermore, the polymer particles have a particle size of 0.5~0.7μm.

[0021] Furthermore, the mass ratio of the first inorganic particle to the second inorganic particle is 6:4 to 7:3.

[0022] Furthermore, the first inorganic particle has a particle size of 80nm~120nm, and the second inorganic particle has a particle size of 0.3μm~0.5μm.

[0023] Furthermore, the particle size of the third inorganic particle is 0.8μm~1.0μm.

[0024] Furthermore, the core layer is polymer A, the shell layer is polymer B, the glass transition temperature Tg1 of the core layer polymer A is 100℃~110℃, and the glass transition temperature Tg2 of the shell layer polymer B is -10℃≤Tg2≤10℃.

[0025] Furthermore, the degree of crosslinking of the core polymer A is X1, and the degree of crosslinking of the shell polymer B is X2, where 5%≤X1≤10% and 50%≤X2≤60%.

[0026] Furthermore, the polymer A accounts for 50% to 80% of the total mass of the polymer particles, and the polymer B accounts for 20% to 50% of the total mass of the polymer particles.

[0027] Furthermore, the elastic modulus of the shell polymer B is E, where 5MPa≤E≤15MPa.

[0028] Furthermore, η1, η2, and η3 satisfy η1 < η2 < η3.

[0029] Furthermore, the swelling rate of the polymer particles is 30%~80% at a low temperature of 60°C and 500%~600% at a high temperature of 120°C.

[0030] Furthermore, the core polymer A accounts for 70% to 80% of the mass of the polymer particles.

[0031] Furthermore, the shell polymer B accounts for 20% to 30% of the total mass of the polymer particles.

[0032] Furthermore, the ratio of the total thickness of the shell layer to the particle size of the entire polymer particle is N, where 10% ≤ N ≤ 20%.

[0033] Furthermore, the polymer A is polymerized from a first polymerizing monomer and a first crosslinking monomer; the first crosslinking monomer accounts for 1% to 5% of the mass of polymer A, preferably 1% to 3%.

[0034] Furthermore, the polymer B is polymerized from a second polymer monomer and a second crosslinking monomer; the second crosslinking monomer accounts for 10% to 15% of the mass of polymer B.

[0035] Furthermore, the glass transition temperature Tg2 of the shell polymer B satisfies -10℃≤Tg2≤5℃.

[0036] Furthermore, the degree of crosslinking X1 of the core polymer A and the degree of crosslinking X2 of the shell polymer B satisfy: 5%≤X1≤8%, 55%≤X2≤60%.

[0037] Furthermore, the elastic modulus E of the shell polymer B satisfies: 5MPa≤E≤12MPa.

[0038] Further, the first polymerizing monomer includes at least one selected from methyl methacrylate, butyl methacrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methacrylonitrile, styrene, acrylonitrile, and methacrylonitrile.

[0039] Further, the second polymerizing monomer includes at least one of ethyl acrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, methyl methacrylate, methacrylonitrile, n-butyl acrylate, or butyl methacrylate.

[0040] Furthermore, the first crosslinking monomer includes at least one of divinylbenzene, diallyl phthalate, diethanol diacrylate, trimethylolpropane trimethacrylate, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0041] Furthermore, the second crosslinking monomer includes at least one of divinylbenzene, diallyl phthalate, diethanol diacrylate, trimethylolpropane trimethacrylate, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0042] Furthermore, the first inorganic particles include at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP.

[0043] Furthermore, the second inorganic particle includes at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP.

[0044] Furthermore, the third inorganic particle includes at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP.

[0045] Furthermore, the first coating also includes an adhesive, accounting for 3% to 6% of the total mass of the first inorganic particles and the second inorganic particles.

[0046] Furthermore, the first coating also includes a dispersant, accounting for 0.2% to 1.0% of the total mass of the first inorganic particles and the second inorganic particles.

[0047] Furthermore, the first coating also includes a wetting agent, accounting for 0.1% to 0.5% of the total mass of the first inorganic particles and the second inorganic particles.

[0048] Furthermore, the second coating also includes a silane coupling agent, accounting for 2% to 5% of the polymer particle mass.

[0049] Furthermore, the second coating also includes an adhesive, comprising 3% to 6% of the mass of the third inorganic particles.

[0050] Furthermore, the second coating also includes a wetting agent, accounting for 0.1% to 0.5% of the mass of the third inorganic particles.

[0051] A method for preparing a non-fluorine coated membrane includes the following steps:

[0052] Step 1: Coat the first mixture onto the base film to obtain the first coating, wherein the first mixture comprises first inorganic particles and second inorganic particles;

[0053] Step 2: Apply the second mixture onto the first coating layer, and then apply the third mixture to obtain the second coating layer. The second mixture comprises a polymer particle emulsion, and the third mixture comprises third inorganic filler particles.

[0054] Furthermore, the second mixture in step 2 also includes a silane coupling agent.

[0055] Furthermore, in step 2, the surface density of the second mixture coating is 0.1 g / m². 2 ~0.2g / m 2 .

[0056] Furthermore, in step 2, the polymer particles include a core layer and a shell layer. The core layer is obtained by polymerization of a monomer including a first polymerizing monomer and a first crosslinking monomer, and the shell layer is obtained by polymerization of a monomer including a second polymerizing monomer and a second crosslinking monomer.

[0057] A secondary battery comprising the above-described non-fluorine coated separator or the non-fluorine coated separator obtained by the above preparation method.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] 1. The non-fluorine coated diaphragm of the present invention is coated with a layer of polymer particles on the surface of the first coating. The polymer particles are selected from special core-shell structure polymers. The polymer particles have low swelling performance at low temperature and high swelling performance at high temperature. They have reversible swelling-shrinkage and heat resistance. The core-shell structure does not collapse after high temperature, thereby improving the heat resistance of the non-fluorine coated diaphragm at high temperature.

[0060] 2. The non-fluorine coated separator of this invention controls the coverage of polymer particles in the composite coating within a certain range. After the non-fluorine coated separator is used to prepare the battery cell, the battery cell operates at low temperatures. The low swelling rate of the polymer particles has almost no effect on the coverage of the polymer particles in the composite coating, so the ion conduction is hardly deteriorated. However, when the battery cell operates at high temperatures, the high swelling rate of the polymer particles increases the coverage of the polymer particles in the composite coating, which seriously blocks the ion conduction. This prevents the internal temperature of the battery cell from further deteriorating and increasing, thereby avoiding the risk of thermal runaway of the battery cell. When the temperature returns to a low temperature, the swelling of the polymer particles decreases, the coverage of the polymer particles in the composite coating decreases, and the battery cell can resume normal operation. The non-fluorine coated separator does not deteriorate the internal resistance and cycle performance of the battery cell, while improving the heat resistance of the non-fluorine coated separator at high temperatures, preventing the battery cell's performance from deteriorating severely, its internal resistance from increasing, and its cycle performance from deteriorating sharply.

[0061] 3. In the non-fluorine coated separator of the present invention, polymer particles are filled inside the second coating. After the non-fluorine coated separator is hot-pressed with the electrode sheet, the polymer particles do not contact the electrode sheet. The inorganic particles on the surface of the coated separator can contact the electrode sheet uniformly, which improves the affinity with the electrolyte. This allows ions on the electrode sheet to be uniformly inserted and removed, thereby improving the cycle performance of the battery cell. Attached Figure Description

[0062] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0063] Figure 1 This is a schematic diagram of the non-fluorine coated diaphragm structure of the present invention;

[0064] Figure 2 This is a scanning electron microscope image of the cross-section of the non-fluorine coated diaphragm of this invention;

[0065] Figure 3 The Tg graph is shown in Example 6 of this invention for polymer particle performance testing.

[0066] Figure labeling: 1-Base film; 2-First coating; 3-Second coating; 4-Polymer particles. Detailed Implementation

[0067] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0068] A non-fluorine coated membrane includes a base membrane and a composite coating coated on at least one side of the base membrane. The composite coating includes a first coating and a second coating, with the first coating disposed between the second coating and the base membrane.

[0069] The first coating comprises first inorganic particles and second inorganic particles;

[0070] The second coating comprises a third inorganic particle and polymer particle;

[0071] The polymer particles are non-fluoropolymers;

[0072] The lower surface of the polymer particles is tangent to the first coating and fills the interior of the second coating.

[0073] If polymer particles are hot-pressed into contact with the electrode sheet, the insertion / extraction of ions at the contact point will be severely hindered, easily leading to lithium plating and ultimately reducing the cell's cycle performance. In this invention, the polymer particles in the non-fluorinated coated separator are filled within the second coating. After hot-pressing the non-fluorinated coated separator with the electrode sheet, the polymer particles do not contact the electrode sheet, allowing the inorganic particles on the surface to uniformly contact the electrode sheet, improving affinity with the electrolyte. This enables uniform insertion / extraction of ions on the electrode sheet, thus improving the cell's cycle performance.

[0074] Preferably, the maximum number of polymer particles connected in phase is N, where N≤8, including but not limited to 1, 2, 3, 4, 5, 6, 7, and 8.

[0075] Preferably, the coverage of polymer particles in the composite coating is η1, 20%≤η1≤35%, where η1 includes, but is not limited to, point values ​​or ranges between point values ​​of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, and 35%.

[0076] Preferably, the non-fluorine coated diaphragm is immersed in an electrolyte at 60°C for 4 hours and then cooled. The coverage of polymer particles in the composite coating is η2, 23%≤η2≤37%, where η2 includes, but is not limited to, point values ​​or ranges between 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, and 37%.

[0077] After immersion in electrolyte at 60℃, the coverage rate η2 of polymer particles in the composite coating satisfies: 23%≤η2≤37%. This is to ensure that the separator still has good air permeability and ion conductivity after hot pressing formation of the battery cell, without affecting subsequent room temperature cycling. The non-fluorinated coated separator and electrode sheets undergo low-temperature hot pressing formation after electrolyte injection. If the low-temperature swelling rate is high, it will affect the formation process. Even with normal battery cell operation, polymer swelling can block ion channels during non-abnormal temperature rises, easily affecting the normal operation of the battery cell. Therefore, a low low-temperature swelling rate is set so that the polymer does not affect the normal operation of the battery cell at low temperatures.

[0078] Preferably, the non-fluorine coated diaphragm is immersed in an electrolyte at 120°C for 4 hours and then cooled. The coverage of polymer particles in the composite coating is η3, which is 38%≤η3≤53%. η3 includes, but is not limited to, point values ​​or ranges between point values ​​of 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, and 53%.

[0079] After immersion in electrolyte at 120℃, the coverage rate η3 of polymer particles in the composite coating satisfies: 38%≤η3≤53%. This is to ensure that after the cell experiences abnormal temperature rise (e.g., close to thermal runaway temperature) and cools down, the membrane performance and subsequent cycle performance are not affected.

[0080] Preferably, η1, η2, and η3 satisfy η1 < η2 < η3.

[0081] This invention controls the coverage of polymer particles in the composite coating within a certain range. After the non-fluorine coated separator is used to prepare the battery cell, the battery cell operates at low temperatures. The low swelling rate of the polymer particles has almost no effect on the coverage of the polymer particles in the composite coating, so the ion conduction is hardly deteriorated. However, when the battery cell operates at high temperatures, the high swelling rate of the polymer particles increases the coverage of the polymer particles in the composite coating, which seriously blocks the ion conduction. This prevents the internal temperature of the battery cell from further deteriorating and increasing, thereby avoiding the risk of thermal runaway of the battery cell. When the temperature returns to a low temperature, the swelling of the polymer particles decreases, the coverage of the polymer particles in the composite coating decreases, and the battery cell can resume normal operation. The non-fluorine coated separator does not deteriorate the internal resistance and cycle performance of the battery cell, while improving the heat resistance of the coated separator at high temperatures, preventing the battery cell's performance from deteriorating severely, its internal resistance from increasing, and its cycle performance from deteriorating sharply.

[0082] If the thickness of the first coating is H1 and the thickness of the second coating is H2, then 0.5≤H1≤1.0μm, where H1 includes, but is not limited to, point values ​​or ranges between point values ​​of 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, and 1μm; and 0.8≤H2≤2.0μm, where H2 includes, but is not limited to, point values ​​or ranges between point values ​​of 0.8μm, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, and 2μm.

[0083] Preferably, the mass ratio of the first inorganic particles to the second inorganic particles in the first coating is 6:4 to 7:3, including but not limited to 6:4, 6.1:3.9, 6.2:3.8, 6.3:3.7, 6.4:3.6, 6.5:3.5, 6.6:3.4, 6.7:3.3, 6.8:3.2, 6.9:3.1, and 7:3.

[0084] Preferably, the particle size of the first inorganic particle is 80nm~120nm, including but not limited to 80nm, 90nm, 100nm, 110nm, and 120nm.

[0085] Preferably, the particle size of the second inorganic particles is 0.3μm to 0.5μm, including but not limited to 0.3μm, 0.4μm, and 0.5μm. The mass ratio of the first inorganic particles and the second inorganic particles in the first coating of the present invention affects the heat resistance and air permeability of the first coating. If the proportion of the first inorganic particles is too large, although it can improve the heat resistance, it will also worsen the air permeability of the coating, leading to an increase in the internal resistance of the battery cell and a decrease in cycle performance. In addition, if the proportion of the first inorganic particles is too large, it is easy to cause the separator edge curling problem, which affects the battery cell manufacturing process. If the proportion of the first inorganic particles is too small, it will lead to a decrease in the heat resistance of the first coating and failure of the battery cell safety performance test.

[0086] The thickness of the second coating of this invention directly affects the performance of the coated diaphragm and the battery cell. The thicker the coating, the greater the overall air permeability, the higher the internal resistance of the battery cell, the lower the ion conduction capacity, and the lower the cycle performance of the battery cell before and after high-temperature treatment. If the coating is too thin, the polymer will swell during high-temperature treatment of the battery cell, and some of it will seep out onto the surface of the second coating and adhere to the electrode, which will make the adhesive part prone to local lithium plating, ultimately affecting the cycle performance.

[0087] Preferably, the particle size of the third inorganic particle is 0.8μm to 1.0μm, including but not limited to 0.8μm, 0.9μm, and 1μm.

[0088] Preferably, the wet-press adhesion force between the non-fluorine coated diaphragm and the electrode sheet is ≤0.5 N / m. When both the wet-press adhesion force and the dry-press adhesion force are close to 0, the non-fluorine coated diaphragm is suitable for applications where adhesion force is not required.

[0089] Preferably, the polymer particles have a core-shell structure, including a core layer and a shell layer. The core layer is polymer A, and the shell layer is polymer B. The glass transition temperature Tg1 of the core polymer A is 100℃~110℃, including but not limited to 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃, and 110℃. The glass transition temperature Tg2 of the shell polymer B is -10℃~10℃, preferably -10℃~5℃, including but not limited to -10℃, -9℃, -8℃, -7℃, -6℃, -5℃, -4℃, -3℃, -2℃, -1℃, 0℃, 1℃, 2℃, 3℃, 4℃, and 5℃.

[0090] The polymer particles of this invention are made of a special core-shell structure polymer. The polymer particles have low swelling performance at low temperatures and high swelling performance at high temperatures. They have reversible swelling-shrinkage and heat resistance. The core-shell structure does not collapse after high temperature, thus improving the heat resistance of non-fluorinated coated membranes at high temperatures.

[0091] Preferably, polymer A accounts for 50% to 80% of the total mass of the polymer particles, and polymer B accounts for 20% to 50% of the total mass of the polymer particles; more preferably, polymer A accounts for 70% to 80% of the total mass of the polymer particles, and the shell polymer B accounts for 20% to 30% of the total mass of the polymer particles, including but not limited to 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, and 30%.

[0092] Preferably, the crosslinking degree of the core polymer A is X1, and the crosslinking degree of the shell polymer B is X2, with 5%≤X1≤10% and 50%≤X2≤60%, more preferably: 5%≤X1≤8%, where X1 includes, but is not limited to, point values ​​of 5%, 6%, 7%, and 8% or the range between point values, and 55%≤X2≤60%, where X2 includes, but is not limited to, point values ​​of 55%, 56%, 57%, 58%, 59%, and 60% or the range between point values.

[0093] Preferably, the elastic modulus of the shell polymer B is E, 5MPa≤E≤15MPa, more preferably 5MPa≤E≤12MPa, and E includes, but is not limited to, point values ​​or ranges between point values ​​of 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa, 11MPa, 12MPa, 13MPa, 14MPa, and 15MPa.

[0094] Preferably, the ratio of the total thickness of the shell to the particle size of the entire polymer particle is N, where 10% ≤ N ≤ 20%.

[0095] Preferably, the polymer particles have a particle size of 0.5~0.7μm, including but not limited to 0.5μm, 0.6μm, and 0.7μm.

[0096] Preferably, the swelling rate of the polymer particles at a low temperature of 60°C is 30% to 80%, including but not limited to 30%, 40%, 50%, 60%, 70%, and 80%, and the swelling rate at a high temperature of 120°C is 500% to 600%, including but not limited to 500%, 510%, 520%, 530%, 540%, 550%, 560%, 570%, 580%, 590%, and 600%.

[0097] Preferably, the polymer particles exhibit a volume recovery rate of ≥90% after high-temperature cooling, possessing reversible swelling-shrinkage and heat resistance, and the core-shell structure does not collapse after high-temperature treatment. Preferably, polymer A is polymerized from a first polymerizing monomer, a first crosslinking monomer, and a small amount of additives; the first crosslinking monomer accounts for 1%~5% of the mass of polymer A, preferably 1%~3%, including but not limited to 1%, 2%, and 3%.

[0098] Preferably, polymer B is polymerized from a second polymer monomer, a second crosslinking monomer and a small amount of additives; the second crosslinking monomer accounts for 10% to 15% of the mass of polymer B, including but not limited to 10%, 12%, 13%, 14% and 15%.

[0099] The first polymerizing monomer includes at least one of methyl methacrylate, 2-ethylhexyl acrylate, methacrylonitrile, styrene, acrylonitrile, methacrylonitrile, butyl methacrylate, and isooctyl acrylate.

[0100] The second monomer includes at least one of ethyl acrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, methyl methacrylate, methacrylonitrile, n-butyl acrylate, or butyl methacrylate.

[0101] The first crosslinking monomer includes at least one of divinylbenzene, diallyl phthalate, diethanol diacrylate, trimethylolpropane trimethacrylate, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0102] The second crosslinking monomer includes at least one of divinylbenzene, diallyl phthalate, diethanol diacrylate, trimethylolpropane trimethacrylate, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0103] The third inorganic particle includes at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO (lithium lanthanum zirconium oxide), and LATP (lithium aluminum titanium phosphate).

[0104] Preferably, the second coating further includes a silane coupling agent, accounting for 2% to 5% of the polymer particle mass, including but not limited to 2%, 3%, 4%, and 5%.

[0105] Silane coupling agents include at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and vinyltrimethoxysilane.

[0106] Preferably, the second coating further includes an adhesive, accounting for 3% to 6% of the mass of the third inorganic particles, including but not limited to 3%, 4%, 5%, and 6%.

[0107] The adhesive includes at least one of epoxy resin, styrene-butadiene rubber, polyacrylate, polyamide, polyacrylonitrile, polyvinyl alcohol, etc.

[0108] Preferably, the second coating further includes a wetting agent, accounting for 0.1% to 0.5% of the mass of the third inorganic particles, including but not limited to 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%.

[0109] The wetting agent includes at least one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene alkylphenol ether, etc.

[0110] The first inorganic particle includes at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO (lithium lanthanum zirconium oxide), and LATP (lithium aluminum titanium phosphate).

[0111] The second inorganic particle includes at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO (lithium lanthanum zirconium oxide), and LATP (lithium aluminum titanium phosphate).

[0112] Preferably, the first coating further includes an adhesive, accounting for 3% to 6% of the total mass of the first inorganic particles and the second inorganic particles, including but not limited to 3%, 4%, 5%, and 6%.

[0113] The adhesive includes at least one of epoxy resin, styrene-butadiene rubber, polyacrylate, polyamide, polyacrylonitrile, polyvinyl alcohol, etc.

[0114] Preferably, the first coating further includes a dispersant, accounting for 0.2% to 1.0% of the total mass of the first inorganic particles and the second inorganic particles, including but not limited to 0.2%, 0.4%, 0.6%, 0.8%, and 1%.

[0115] The dispersant includes at least one of sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, alkylbenzene sulfonate, etc.

[0116] Preferably, the first coating further includes a wetting agent, accounting for 0.1% to 0.5% of the total mass of the first inorganic particles and the second inorganic particles, including but not limited to 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%.

[0117] The wetting agent includes at least one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene alkylphenol ether, etc.

[0118] A method for preparing a non-fluorine coated membrane includes the following steps:

[0119] Step 1: Coat the first mixture onto the base film to obtain the first coating, wherein the first mixture comprises first inorganic particles and second inorganic particles;

[0120] Step 2: Apply the second mixture onto the first coating layer, and then apply the third mixture to obtain the second coating layer. The second mixture comprises a polymer particle emulsion, and the third mixture comprises third inorganic filler particles.

[0121] Preferably, the second mixture in step 2 further includes a silane coupling agent. The silane coupling agent can optimize the dispersion stability of the slurry, allowing the polymer particles to be uniformly coated on the diaphragm.

[0122] Preferably, the surface density of the second mixture coating in step 2 is 0.1 g / m². 2 ~0.2g / m 2 Including but not limited to 0.1g / m 2 0.11g / m 2 0.12g / m 2 0.13g / m 2 0.14g / m 2 0.15g / m 2 0.16g / m 2 0.17g / m 2 0.18g / m 2 0.19g / m 2 0.2g / m 2 .

[0123] Preferably, in step 2, the polymer particles include a core layer and a shell layer. The core layer is obtained by polymerization of a monomer including a first polymerizing monomer and a first crosslinking monomer, and the shell layer is obtained by polymerization of a monomer including a second polymerizing monomer and a second crosslinking monomer.

[0124] A secondary battery comprising the above-described non-fluorine coated separator or the non-fluorine coated separator obtained by the above preparation method.

[0125] Example 1

[0126] A method for preparing a non-fluorine coated membrane includes the following steps:

[0127] Step 1: Preparation of polymer particle core layer: Add 200 parts of deionized water and 0.5 parts of sodium dodecylbenzenesulfonate to the reaction vessel, stir evenly, purge the air in the reaction vessel with nitrogen, add 67.1 parts of acrylonitrile, 6.7 parts of 2-ethylhexyl acrylate and 1.2 parts of diethanol diacrylate, adjust the pH of the reaction to 7.0~8.0, raise the core layer reaction temperature and pressure to 85℃ and 2.0MPa respectively, add 1.0 part of sodium persulfate, and react for 4h;

[0128] Step 2, preparation of polymer particle emulsion: Add 2.8 parts acrylonitrile, 19.1 parts 2-ethylhexyl acrylate and 3.1 parts diethanol diacrylate to the above reaction vessel, adjust the shell reaction temperature and pressure to 75℃ and 4.0MPa, and continue the reaction for a period of time. Then, cool down and reduce the pressure to obtain polymer particle emulsion (test polymer particle size, Tg, and high and low temperature swelling).

[0129] Step 3, Preparation of the first mixture: Take 63 parts of boehmite with a particle size of 100 nm, 37 parts of boehmite with a particle size of 0.40 μm, 250 parts of deionized water and 0.6 parts of sodium tripolyphosphate, sonicate with a 2 kW ultrasonic machine for 30 min, then add 5 parts of polyacrylate and 0.4 parts of polyoxyethylene alkylphenol ether, stir evenly to obtain the first mixture;

[0130] Step 4, Preparation of the second mixture: Take 100 parts of polymer particle emulsion, 500 parts of deionized water, 0.5 parts of γ-aminopropyltriethoxysilane and 0.1 parts of polyoxyethylene alkylphenol ether, mix them, stir evenly, and obtain the second mixture;

[0131] Step 5, Preparation of the third mixture: Take 100 parts of boehmite with a particle size of 0.90 μm, 150 parts of deionized water, 0.2 parts of sodium tripolyphosphate, 4 parts of polyacrylate and 0.2 parts of polyoxyethylene alkylphenol ether, mix them, stir evenly to obtain the third mixture;

[0132] Step 6: Preparation of non-fluorine coated separator: Take the first mixture, use microgravure coating technology, adjust the microgravure coating speed ratio, coat the first mixture onto the lithium battery separator, and dry it to obtain an areal density of 0.82 g / m³. 2 The first coating layer is applied; then, a second mixture is applied, and using the same microgravure coating technique with the coating speed ratio adjusted, the second mixture is coated onto the first coating layer, resulting in an areal density of 0.15 g / m². 2 The polymer coating was then applied; finally, the third mixture was taken and coated onto the first and polymer coatings using the same microgravure coating technique, with the microgravure coating speed ratio adjusted, resulting in an areal density of 0.98 g / m³. 2The second coating is then applied to obtain a non-fluorine coated diaphragm.

[0133] The test included the air permeability growth rate, first / second coating thickness, maximum number of polymer connections, polymer particle coverage η1 / η2 / η3 in the composite coating, room temperature ionic conductivity, wet pressure adhesion, and the cycle performance, safety, and lithium plating issues of the non-fluorine coated separator after it was made into a battery cell.

[0134] Example 2

[0135] Compared to Example 1, in step 4, during the preparation of the second mixture, 100 parts of polymer particle emulsion, 450 parts of deionized water, 0.5 parts of γ-aminopropyltriethoxysilane, and 0.1 parts of polyoxyethylene alkylphenol ether were mixed; in step 6, during membrane coating, the speed ratio was adjusted to obtain a coating layer density of 0.15 g / m² for the second mixture. 2 The non-fluorine coated diaphragm is the same as in Example 1.

[0136] Example 3

[0137] Compared to Example 1, in step 4, during the preparation of the second mixture, 100 parts of polymer particle emulsion, 600 parts of deionized water, 0.5 parts of γ-aminopropyltriethoxysilane, and 0.1 parts of polyoxyethylene alkylphenol ether were mixed; in step 6, during membrane coating, the speed ratio was adjusted to obtain a coating layer density of 0.15 g / m² for the second mixture. 2 The non-fluorine coated diaphragm is otherwise the same as in Example 1.

[0138] Example 4

[0139] Compared to Example 1, in step 2, when preparing the polymer particle emulsion, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 2.3 parts, 19.2 parts, and 3.5 parts, respectively, while other steps were the same as in Example 1.

[0140] Example 5

[0141] Compared to Example 1, in step 2, when preparing the polymer particle emulsion, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in the amounts of 3.6 parts, 18.7 parts, and 2.7 parts, respectively, while other steps were the same as in Example 1.

[0142] Example 6

[0143] Compared to Example 1, in step 1, when preparing the polymer particle core layer, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 66.3 parts, 6.7 parts, and 2.0 parts, respectively. In step 2, when preparing the polymer particle emulsion, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 3.5 parts, 18.4 parts, and 3.1 parts, respectively. The other steps were the same as in Example 1.

[0144] Example 7

[0145] Compared to Example 1, in step 1, when preparing the polymer particle core layer, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 68.0 parts, 6.2 parts, and 0.8 parts, respectively. In step 2, when preparing the polymer particle emulsion, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 2.6 parts, 19.3 parts, and 3.1 parts, respectively. The other steps were the same as in Example 1.

[0146] Comparative Example 1

[0147] Compared to Example 1, in step 4, during the preparation of the second mixture, 100 parts of polymer particle emulsion, 300 parts of deionized water, 0.5 parts of γ-aminopropyltriethoxysilane, and 0.1 parts of polyoxyethylene alkylphenol ether were mixed; in step 6, during membrane coating, the speed ratio was adjusted to obtain a coating layer density of 0.15 g / m² for the second mixture. 2 The non-fluorine coated diaphragm is otherwise the same as in Example 1.

[0148] Comparative Example 2

[0149] Compared to Example 1, in step 6, the preparation of the non-fluorine coated membrane utilizes microgravure coating technology when coating the second mixture. The microgravure coating speed ratio is adjusted to coat the second mixture onto the first coating layer, resulting in an areal density of 0.24 g / m³. 2 The polymer coating is the same as in Example 1.

[0150] Comparative Example 3

[0151] Compared to Example 1, in step 6, the preparation of the non-fluorine coated membrane utilizes microgravure coating technology when coating the second mixture. The microgravure coating speed ratio is adjusted to coat the second mixture onto the first coating layer, resulting in an areal density of 0.08 g / m³. 2 The polymer coating is the same as in Example 1.

[0152] Comparative Example 4

[0153] Compared to Example 1, in step 1, when preparing the polymer particle core layer, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 66.1 parts, 7.7 parts, and 1.2 parts, respectively. In step 2, when preparing the polymer particle emulsion, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 2.8 parts, 15.2 parts, and 7.0 parts, respectively. The other steps were the same as in Example 1.

[0154] Comparative Example 5

[0155] Compared to Example 1, in step 1, when preparing the polymer particle core layer, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 67.2 parts, 6.6 parts, and 1.2 parts, respectively. In step 2, when preparing the polymer particle emulsion, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 3.4 parts, 20.2 parts, and 1.4 parts, respectively. The other steps were the same as in Example 1.

[0156] Comparative Example 6

[0157] Compared to Example 1, in step 1, when preparing the polymer particle core layer, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 64.9 parts, 6.9 parts, and 3.2 parts, respectively, while other steps were the same as in Example 1.

[0158] Comparative Example 7

[0159] Compared to Example 1, in step 1, when preparing the polymer particle core layer, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 67.9 parts, 6.9 parts, and 0.2 parts, respectively. In step 2, when preparing the polymer particle emulsion, acrylonitrile, 2-ethylhexyl acrylate, and diethanol diacrylate were taken in amounts of 2.6 parts, 19.3 parts, and 3.1 parts, respectively. The other steps were the same as in Example 1.

[0160] The physical parameters of the polymer particles in the examples and comparative examples are shown in Table 1.

[0161] Table 1 Physical parameters of polymer particles in the examples and comparative examples

[0162]

[0163] Experimental example:

[0164] I. Polymer particle performance test results are shown in Table 2.

[0165] 1. Tg Test: Dry the polymer emulsions and weigh 4-8 mg of each sample. Measure the Tg using differential scanning calorimetry (DSC). Test equipment: METTLER DSC3; test temperature range: -80~200℃; heating rate: 10℃ / min. After the test, integrate the curve to obtain the Tg of the polymer particle emulsion. After the test, integrate the curve to obtain Tg1 for the core polymer emulsion and Tg2-1 and Tg2-2 for the non-fluorinated polymer emulsion (one of Tg2-1 and Tg2-2 is the core layer Tg, i.e., Tg1, and the other is the shell layer Tg2).

[0166] 2. Particle size test: Take polymer particle emulsion and drop it into Malvern 3000 to test the particle size. The test results are: refractive index: 1.50, absorptivity: 0.1, and opacity: 10%~18%, to obtain the particle size D50 of the polymer.

[0167] 3. Polymer swelling test: Dry the polymer particle emulsion to obtain a gel film. Take a certain amount of electrolyte (EC:EP:DEC=1:1:3, 1.0 Mol / L LiPF6) in a graduated container and read the electrolyte volume V1. Add 5g of the gel film to the container, immersing the gel film in the electrode solution, and read the volume V2 at this time. Seal the container and place it in a 60℃ oven for 4 hours. Remove the gel film quickly and read the volume V3 of the remaining electrode solution in the container. The swelling rate of the gel film at 60℃ is W1=(V2-V3) / (V2-V1). Use the same method to test the swelling rate of the gel film at 120℃, W2=(V2-V3) / (V2-V1).

[0168] 4. Core layer polymer crosslinking degree test: Dry the core layer polymer emulsion, weigh a certain mass of film M1, immerse the film in tetrahydrofuran reagent, soak at room temperature for 72 hours, take out the film, wash the film three times with alcohol, then dry the film, weigh the mass of the dried film M2, then the crosslinking degree of the core layer polymer X1=M2 / M1.

[0169] 5. Test of crosslinking degree of shell polymer: Take the polymer particle emulsion and dry it. Weigh a certain mass of film m1 (assuming the shell ratio is P, then the shell mass is P*m1, and the core mass is m1-P*m1, where P can be calculated from the total mass of the core monomers and the total mass of the shell monomers added during the synthesis of non-fluorinated polymers). Soak the film in tetrahydrofuran reagent for 72 hours. Take out the film, wash the film three times with alcohol, and then dry the film. Weigh the mass of the dried film m2. Then the crosslinking degree of the core polymer X2 = (m2-(1-P)*m1*X1) / (P*m1).

[0170] 6. Shell elastic modulus: The shell elastic modulus of polymer particles was tested using an FT-NMT04 in-situ nanoindenter with a Berkovich indenter. The loading and unloading times were both set to 2 seconds. The relationship between load and displacement was established, and the final elastic modulus was calculated using the Oliver principle. Ten polymer particles were tested in parallel, and the final average value E was taken.

[0171] II. Performance test of non-fluorine coated diaphragm. The test results are shown in Table 3.

[0172] 1. Air permeability growth rate: (Air permeability refers to the time required for 100ml of gas to pass through a membrane with a fixed area. Air permeability growth rate = (air permeability of coated membrane - air permeability of base membrane) / air permeability of base membrane * 100%).

[0173] 2. Thickness of the first / second coating: The non-fluorine coated membrane is cut perpendicular to the membrane plane using an ion polisher to obtain the cross-section of the non-fluorine coated membrane. The thickness of the first and second coatings of the cross-section is tested under a scanning electron microscope at 10,000 magnification. Five points are randomly tested on the same sample, and the average value is taken. Six samples are tested in parallel using the same method, and the final average value is taken as the thickness of the first and second coatings.

[0174] 3. Maximum number of connected polymer particles N: The non-fluorine coated membrane is cut perpendicular to the membrane plane using an ion polisher to obtain the composite membrane cross-section. Ten points are selected under a scanning electron microscope at 5000x magnification, and the maximum number of connected polymer particles is counted at each point. The largest connected number value among the ten points is taken. The same method is used to test ten samples, and the maximum number of connected polymer particles in the ten samples is compared. This is the maximum number of connected polymer particles N in the non-fluorine coated membrane.

[0175] 4. Coverage of polymer particles in the composite coating, η1, η2, η3:

[0176] 4.1 Polymer particle coverage η1 test in composite coating: Take a non-fluorine coated diaphragm and take an electron microscope with the cut surface perpendicular to the membrane plane. Randomly select 10 points and measure the longest particle size of the polymer parallel to the diaphragm surface at 8000x magnification (16.0μm*12.0μm). Add up the lengths of all polymer particles and divide by the length at this magnification of 16μm to obtain the coverage of polymer particles in composite coating. Take the average value of these 10 points. Test 10 samples in the same way and take the average value. This is the coverage of polymer particles in composite coating η1.

[0177] 4.2 Test of polymer particle coverage η2 in composite coating: Take a non-fluorine coated diaphragm and immerse it in an electrolyte (EC:EP:DEC=1:1:3, 1.0 Mol / L LiPF6) at 60℃ for 4 hours. Take it out and dry it. The test method is the same as η1 to obtain η2.

[0178] 4.3 Test of polymer particle coverage η3 in composite coating: Take a non-fluorine coated diaphragm and immerse it in an electrolyte (EC:EP:DEC=1:1:3, 1.0 Mol / L LiPF6) at 120℃ for 4 hours. Take it out and dry it. The test method is the same as η1 to obtain η3.

[0179] 5. Ion conductivity performance at room temperature: (In an argon-filled glove box, the membrane was made into a 2016 button cell, and an appropriate amount of electrolyte (EC:EP:DEC=1:1:3, 1.0 Mol / L LiPF6) was added. The AC impedance was measured using an electrochemical workstation. The result is σ=L / (Rb*A), where σ is the ion conductivity at room temperature (mS / cm); L is the membrane thickness (cm); Rb is the intrinsic resistance of the membrane (Ω); and A is the effective area (cm²). 2 ).

[0180] 6. Wet pressure test of non-fluorine coated diaphragm: Take a non-fluorine coated diaphragm and attach it to the electrode sheet, then hot press it at 5MPa and 85℃ for 5min. Take out the composite of electrode sheet and diaphragm, tighten the electrode sheet and diaphragm with a steel plate of the same size, and tighten it with a clamp of 1MPa. Immerse it in electrolyte (EC:EP:DEC=1:1:3, 1.0 Mol / L LiPF6) for 4h. Take it out and wipe off the electrolyte on the surface. Test the adhesion between the diaphragm and the electrode sheet by peeling it at 180°.

[0181] III. Electrical performance test results are shown in Table 4.

[0182] 1. Capacity retention test:

[0183] 1.1 Cell Normal Operation Capacity Retention Rate Test: The cell is fabricated using a stacking process with a non-fluorine coated separator, lithium iron phosphate positive electrode, and graphite negative electrode. The battery is charged at a constant current of 0.5C to 3.6V, then charged at a constant voltage of 3.6V until the current reaches 0.02C, charging is terminated, and the battery is allowed to rest for 30 minutes. It is then discharged at a constant current of 0.5C to 2.0V, the discharge is terminated, and the battery is allowed to rest for 30 minutes. The first discharge capacity is recorded. This cycle is repeated 450 times, and the discharge capacity on the 450th cycle is recorded. The ratio of the 450th cycle discharge capacity to the first cycle discharge capacity is the battery's capacity retention rate after 450 cycles.

[0184] 1.2 Capacity Retention Rate Test After High-Temperature Treatment of Battery Cells: Battery cells were fabricated using a stacking process with a non-fluorine-coated separator, lithium iron phosphate positive electrode, and graphite negative electrode. The battery was charged at a constant current of 0.5C to 3.6V, then charged at a constant voltage of 3.6V until the current reached 0.02C, charging was terminated, and the cells were allowed to stand for 30 minutes. The cells were then discharged at a constant current of 0.5C to 2.0V, the discharge was terminated, and the cells were allowed to stand for 30 minutes. The first discharge capacity was recorded. After discharge, the cells were placed in a 120℃ oven and baked for 1 hour. They were then removed and allowed to stand for 24 hours. The cells were then cycled through 450 times using the same parameters as the first cycle. The discharge capacity of the 450th cycle was recorded. The ratio of the 450th cycle discharge capacity to the first cycle discharge capacity was used to determine the capacity retention rate of the battery cells after 450 cycles of high-temperature treatment.

[0185] 2. Lithium plating in the battery cell: Take the battery cell from section 1.1 above after 450 cycles of capacity retention testing, disassemble it, and record the lithium plating status of the battery cell.

[0186] 3. Safety Performance Test: A cell is fabricated using a stacking process with a non-fluorine coated separator, lithium iron phosphate positive electrode, and graphite negative electrode. After fully charging, the battery is placed in an oven. The oven is heated at 10℃ / min to 110℃ and held for 30 minutes, then at 1℃ / min to 120℃ and held for 30 minutes, then at 1℃ / min to 130℃ and held for 30 minutes, then at 1℃ / min to 140℃ and held for 30 minutes, and finally at 1℃ / min to 150℃ and held for 30 minutes. If the cell explodes or catches fire, the battery safety performance is deemed unsuccessful. If the battery explodes or catches fire as the temperature rises, the experiment is terminated, and the battery safety performance is deemed unsuccessful. The safety performance of 10 batteries is tested in parallel using the same method. The cell safety test pass rate is calculated as: (Number of passing cells / 10) * 100%.

[0187] Table 2 Polymer Particle Performance Test Data

[0188]

[0189] Table 3 Test data for non-fluorinated coated membranes

[0190]

[0191] Table 4 Performance test data of cells made with non-fluorine coated separators

[0192]

[0193] The parameters of the polymer particles and coated separators described in Examples 1-7 are all within the range of the present invention, and both the coated separators and the battery cells exhibit good performance.

[0194] In Comparative Example 1, the high maximum number of polymer particles connected together resulted in low ionic conductivity and localized lithium plating in the cell. In Comparative Example 2, the polymer coating surface density was too high, leading to excessive coverage of polymer particles in the composite coating, increased coating permeability, decreased ionic conductivity, and partial penetration of the binder to the surface and adhesion to the electrode at high temperatures, resulting in decreased cell performance and lithium plating. In Comparative Example 3, the polymer coating surface density was too low, resulting in insufficient coverage of polymer particles in the composite coating and a reduced cell safety performance pass rate. In Comparative Example 4, the high degree of cross-linking of the polymer shell resulted in low polymer swelling rate at high temperatures, and the polymer particles in the composite coating... The low coverage of the polymer core layer in Comparative Example 5 resulted in a low pass rate for cell safety performance. In Comparative Example 6, the high cross-linking degree of the polymer core layer resulted in a low polymer swelling rate at high temperatures, leading to excessive coverage of polymer particles in the composite coating. Some of these particles penetrated to the surface and adhered to the electrode, reducing capacity retention and causing lithium plating in the cell. In Comparative Example 7, the low cross-linking degree of the polymer core layer resulted in a high polymer swelling rate at high temperatures, causing the polymer particles to break through the shell layer, penetrate to the surface and adhere to the electrode, reducing capacity retention and causing lithium plating in the cell.

Claims

1. A non-fluorine coated diaphragm, characterized in that, The system comprises a base film and a composite coating coated on at least one side of the base film, the composite coating comprising a first coating and a second coating, the first coating being disposed between the second coating and the base film; The first coating comprises first inorganic particles and second inorganic particles; The second coating comprises third inorganic particles and polymer particles; The polymer particles are non-fluoropolymers; The lower surface of the polymer particles is tangent to the first coating and fills the interior of the second coating; The maximum number of polymer particles connected in phase is N, where N≤8; The coverage of the polymer particles in the composite coating is η1, where 20% ≤ η1 ≤ 35%; The thickness of the second coating is H2, where 0.8 ≤ H2 ≤ 2.0 μm; The polymer particles have a particle size of 0.5~0.7μm; The polymer particles have a core-shell structure, including a core layer and a shell layer; The core layer is polymer A, the shell layer is polymer B, the glass transition temperature Tg1 of the core layer polymer A is 100℃~110℃, and the glass transition temperature Tg2 of the shell layer polymer B is -10℃≤Tg2≤10℃. The degree of crosslinking of the core polymer A is X1, and the degree of crosslinking of the shell polymer B is X2, where 5% ≤ X1 ≤ 10% and 50% ≤ X2 ≤ 60%. The polymer particles have a swelling rate of 30% to 80% at a low temperature of 60°C and a swelling rate of 500% to 600% at a high temperature of 120°C.

2. The non-fluorine coated diaphragm according to claim 1, characterized in that, It should include at least one of the following technical features: (1) The non-fluorine coated diaphragm is immersed in an electrolyte at 60°C for 4 hours and then cooled. The coverage of polymer particles in the composite coating is η2, 23%≤η2≤37%; (2) The non-fluorine coated diaphragm is immersed in an electrolyte at 120°C for 4 hours and then cooled. The coverage of polymer particles in the composite coating is η3, 38%≤η3≤53%; (3) The thickness of the first coating is H1, 0.5≤H1≤1.0μm; (4) The wet pressure adhesion force between the non-fluorine coated diaphragm and the electrode sheet is ≤0.5N / m.

3. The non-fluorine coated diaphragm according to claim 2, characterized in that, It should include at least one of the following technical features: (1) The mass ratio of the first inorganic particle to the second inorganic particle is 6:4 to 7:3; (2) The first inorganic particle has a particle size of 80nm~120nm, and the second inorganic particle has a particle size of 0.3μm~0.5μm; (3) The particle size of the third inorganic particle is 0.8μm~1.0μm.

4. The non-fluorine coated diaphragm according to claim 3, characterized in that, It should include at least one of the following technical features: (1) The mass of polymer A accounts for 50% to 80% of the total mass of the polymer particles, and the mass of polymer B accounts for 20% to 50% of the total mass of the polymer particles; (2) The elastic modulus of the shell polymer B is E, 5MPa≤E≤15MPa; (3) eta1, eta2, and eta3 satisfy eta1<eta2<eta3.

5. The non-fluorine coated diaphragm according to claim 4, characterized in that, It should include at least one of the following technical features: (1) The core polymer A accounts for 70% to 80% of the mass of the polymer particles; (2) The shell polymer B accounts for 20% to 30% of the total mass of the polymer particles; (3) The ratio of the total thickness of the shell layer to the particle size of the entire polymer particle is N, where 10% ≤ N ≤ 20%; (4) The polymer A is polymerized from a first polymerizing monomer and a first crosslinking monomer; the first crosslinking monomer accounts for 1% to 5% of the mass of polymer A; (5) The polymer B is polymerized from a second polymer monomer and a second crosslinking monomer; the second crosslinking monomer accounts for 10% to 15% of the mass of polymer B; (6) The glass transition temperature Tg2 of the shell polymer B satisfies -10℃≤Tg2≤5℃; (7) The degree of crosslinking X1 of the core polymer A and the degree of crosslinking X2 of the shell polymer B satisfy: 5%≤X1≤8%, 55%≤X2≤60%; (8) The elastic modulus E of the shell polymer B satisfies: 5MPa≤E≤12MPa.

6. The non-fluorine coated diaphragm according to claim 5, characterized in that, It should include at least one of the following technical features: (1) The first polymerizing monomer includes at least one of methyl methacrylate, butyl methacrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methacrylonitrile, styrene, acrylonitrile, and methacrylonitrile; (2) The second polymerizing monomer includes at least one of ethyl acrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, methyl methacrylate, methacrylonitrile, n-butyl acrylate or butyl methacrylate; (3) The first crosslinking monomer includes at least one of divinylbenzene, diallyl phthalate, diethanol diacrylate, trimethylolpropane trimethacrylate, vinyltriethoxysilane, and vinyltrimethoxysilane; (4) The second crosslinking monomer includes at least one of divinylbenzene, diallyl phthalate, diethanol diacrylate, trimethylolpropane trimethacrylate, vinyltriethoxysilane, and vinyltrimethoxysilane; (5) The first inorganic particles include at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP; (6) The second inorganic particle includes at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP; (7) The third inorganic particle includes at least one of boehmite, alumina, magnesium hydroxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP.

7. The non-fluorine coated diaphragm according to claim 1, characterized in that, It should include at least one of the following technical features: (1) The first coating also includes an adhesive, accounting for 3% to 6% of the total mass of the first inorganic particles and the second inorganic particles; (2) The first coating further includes a dispersant, accounting for 0.2% to 1.0% of the total mass of the first inorganic particles and the second inorganic particles; (3) The first coating further includes a wetting agent, accounting for 0.1% to 0.5% of the total mass of the first inorganic particles and the second inorganic particles; (4) The second coating also includes a silane coupling agent, accounting for 2% to 5% of the polymer particle mass; (5) The second coating also includes an adhesive, accounting for 3% to 6% of the mass of the third inorganic particles; (6) The second coating also includes a wetting agent, accounting for 0.1% to 0.5% of the mass of the third inorganic particles.

8. A method for preparing a non-fluorine coated diaphragm as described in any one of claims 1 to 7, characterized in that: Includes the following steps: Step 1: Coat the first mixture onto the base film to obtain the first coating, wherein the first mixture comprises first inorganic particles and second inorganic particles; Step 2: Apply the second mixture onto the first coating layer, and then apply the third mixture to obtain the second coating layer. The second mixture comprises a polymer particle emulsion, and the third mixture comprises third inorganic filler particles.

9. The method for preparing the non-fluorine coated diaphragm according to claim 8, characterized in that: It should include at least one of the following technical features: (1) The second mixture in step 2 also includes a silane coupling agent; (2) The surface density of the second mixture coating in step 2 is 0.1 g / m³. 2 ~0.2g / m 2 ; (3) In step 2, the polymer particles include a core layer and a shell layer. The core layer is obtained by polymerization of a monomer including a first polymerizing monomer and a first crosslinking monomer, and the shell layer is obtained by polymerization of a monomer including a second polymerizing monomer and a second crosslinking monomer.

10. A secondary battery, comprising a non-fluorine coated separator as described in any one of claims 1 to 7 or a non-fluorine coated separator obtained by the preparation method as described in claim 8 or 9.

Images